These are easily bypassed with chips.
There are two reasons I can think of right away for limiting the top speed of a vehicle.
One is tires, and the speed rating they have from the factory.
The second, and one that is a lot more difficult to fix, is drivetrain torsional rigidity. There has been a great deal of discussion about this recently on the Thunderbird bulletin board I follow.
Most any 89-up T-bird is capable of exceeding the 105 mph governor the factory puts in all but the Super Coupes and Mark 8 Lincolns. There's a guy named Jerry Wroblewski who posts on it all the time. He's a powertrain engineer, and gets in on a lot of Ford's wild projects. The biggest problem is driveshaft rotational speed vs. the type of metal used, the stiffness inherent in the rest of the drivetrain, etc. Lincolns use an aluminum driveshaft, the Super Coupe uses an aluminum oil pan on the engine, and the 5 speed SC's get 2.73 gears, vs. 3.08 or 3.27 for automatics.
Check out the board and look for his posts. Full of info if you're into Fords. www.tccoa.com
technical bulletin board